I used grocery store newspaper adds and hung them around the room. I whited out some prices, like $5 to $4.39 to make it harder. I then timed teams to see who could get the most groceries for $20 without going over or who could get the least groceries without going over. You can change the value and do many different variations. I added a coupon area just to make things harder. I created my own coupon, i.e. 20% off, by one get one free, etc. My students loved it. It was a good lesson on estimating.